1. Field of the Invention
The present invention relates to apparatus for measuring an angular velocity variation rate (viz., angular acceleration) of a rotary axle applicable to, for example, an apparatus for detecting a torque of an oscillation-type chassis dynamometer and applicable to cases where an electric inertia simulation is carried out without use of a mechanical variable inertia device and where velocity fluctuations are suppressed in an electric motor having many load variations.
2. Description of the Related Art
An angular velocity variation rate (i.e. angular acceleration or deceleration) is an important control parameter when electric inertia control is carried out in a chassis dynamometer.
Japanese Patent Application First Publication No. Heisei 5-322,924 published on Dec. 7, 1993 (now Japanese Patent No. 2,500,565) exemplifies an analog-type angular velocity variation rate measuring apparatus.
In the analog-type angular velocity variation rate measuring apparatus disclosed in the above-described Japanese Patent First Publication, a pair of pulse pick-ups are disposed concentrically around an inductor attached onto the rotary axle on a virtual line passing a center of the rotary axle with one of the pulse (magnetic) pick-ups disposed in a positional phase difference of 180xc2x0 to the other. A frequency (a repetition rate) of a revolution velocity pulse train proportional to a revolution velocity of the rotary axle generated by means of each pulse pick-up, is then converted into an analog velocity indicative signal to derive an average value by means of a frequency-to-voltage converter. Each analog velocity indicative signal is averaged and the averaged analog velocity indicative signal is differentiated by means of a differentiator to provide an angular velocity variation rate indicative signal. Since the pair of the pulse pickups are disposed around the inductor at a pulse interval of 180xc2x0, a measurement error due to an eccentricity of the inductor to the rotary axle can be cancelled.
However, in the frequency-to-voltage converter used in the analog angular velocity variation rate measuring apparatus, the linearity of the conversion of the frequency to the voltage is reduced in a relatively low frequency range.
In addition, in an electrical inertia control such as carried out in the chassis dynamometer, a rated angular acceleration measurement range is extremely small and a zero point stability is degraded. For example, in a chassis dynamometer having rollers each roller having a diameter on which vehicular road wheels are mounted, a normal rated velocity is about 160 Km/h (=44.4 m/s and the roller revolution speed is 11.67sxe2x88x921) and a rated angular velocity variation rate measurement range is about xc2x15 m/s2.
That is to say, it takes eight seconds or longer to accelerate the roller up to the rated velocity.
A differentiator, provided in the above-described analog type velocity variation rate measuring apparatus, to calculate the angular acceleration from the angular velocity is constituted by a first capacitor interposed between an angular velocity input and a first resistor , a second resistor connected across a first operational amplifier, a second capacitor connected across the first operational amplifier, a third resistor, a variable resistor connected to the first operational amplifier, and a second operational amplifier across which the variable resistor is connected and which outputs the angular velocity variation rate. If a differentiation time is obtained within a time on the basis of which the above-described velocity variation rate is derived, the first capacitor indicates approximately 4 xcexcF and the first resistor indicates approximately 250 kilo-ohms.
Although the measurement accuracy is reduced if a film capacitor having a small leakage resistance is not used as the first capacitor, an actual mounting limit of 4 xcexcF is present in terms of dimension of the first capacitor. If the angular velocity signal voltage inputted into the differentiator is 10 V at 160 Km/h, a voltage variation rate at the differentiator indicates xc2x11.2 V/s. An input current to the differentiator is 1.2xc3x974xc3x9710xe2x88x926=about 0.005 mA. This current value is relatively small as compared with about 0, 2 mA which is the input current at the rated velocity to prevent a variation due to a temperature variation and an external noise interference in a normally available analog controller. Consequently, a stability at a zero point becomes worsened.
The differentiator requires insertions of the second capacitor and the second resistor in order to prevent the detrimental effect of external noise and to prevent self oscillation from occurring.
Consequently, the response rate is degraded. An experimental result indicated that a maximum limit of 30 ms was placed at a response time percentage of 63%.
The analog-type angular velocity variation rate measuring apparatus described above under the heading of xe2x80x9crelated artxe2x80x9d suffers from a number of drawbacks. In order to improve the measuring accuracy of the angular velocity variation rate with the above-described problems eliminated, a digital type angular velocity variation rate measuring apparatus has been proposed.
This previously proposed digital angular acceleration (angular velocity variation rate) measuring apparatus includes: an inductor of a toothed gear type attached concentrically onto the rotary axle; the pair of same pulse pick-ups whose disposed positions are the same as described in the case of the analog type velocity variation rate measuring apparatus; a pair of pulse shapers, each shaper shaping the corresponding velocity pulse signal from the corresponding pick-up of the first pair; a pair of velocity pulse counters counting the shaped velocity pulse signal from the pair of pulse shapers; a pair of period measuring counters, each period measuring counter receiving a velocity pulse from the corresponding pulse pick-up to count the velocity pulse signal; a memory to store a result of measurement corresponding to a predetermined number of times upon a receipt of the velocity pulse counters and the period measuring counters; an angular velocity calculator to calculate an average angular velocity upon receipt of the output of the memory; a controller to control the memory and the angular velocity calculator; a pair of digital-to-analog converters to convert the angular velocity and the angular acceleration calculated into digital signal. The digital-to-analog converter converts the angular velocity and the angular velocity variation rate into the digital signal. A first angular velocity variation rate calculating section is constituted by each circuit subsequent to the pair of pulse shapers.
As described above, each pulse pick-up generates magnetically the velocity pulse in synchronization with a revolution of the inductor. After the velocity pulse is shaped by means of the pair of pulse shapers, the number of velocity pulses is counted by means of each velocity pulse counter and is stored into an output register storing the accumulated number of velocity pulses.
Whenever the velocity pulses are inputted, the contents of the output register are updated. Each period measuring counts the number of clock pulses and is stored into the output register storing the number of accumulated clock pulses. Whenever the velocity pulse is inputted, the count of the output register is updated.
The controller, whenever the period measuring clock is inputted, issues a read command to the memory to store a latest measurement value stored into each output register of the corresponding counter, viz., the accumulated clock pulse number. Thereafter, the controller issues a calculation command to the angular velocity calculating section to read the latest accumulated velocity pulse number from the memory. The controller, thus, calculates the latest average angular velocity from the previously measured corresponding data, outputs the latest average angular velocity from the previously measured corresponding data and outputs it to the digital-to-analog converter, the average angular velocity being accumulatively stored into the memory. Thereafter, a calculation end signal is outputted to the angular velocity variation rate calculating section.
The angular velocity variation rate calculating section receives the calculation end signal to the latest accumulated check pulses and the average angular velocity from the memory.
The angular acceleration is calculated from this data and from the corresponding data before the number of times of measurement n settable arbitrarily and is outputted to the digital-to-analog converter converts the digital value to the analog value so as to output the digital angular velocity signal and the angular velocity variation rate signal.
Since, in the previously proposed digital angular velocity variation rate measuring apparatus described above, analog circuits such as the frequency-to-voltage converter are not used, a reduction of the linearity characteristic in the relatively low frequency region, an instability characteristic at zero point, and a slowing of the response rate can be prevented. In addition, since the angular velocity variation rate is derived from an inversion of the period of the velocity pulse train signal, an extremely small velocity measurement resolution can be obtained even at a short measuring period. The measurement period of the previously proposed digital angular velocity rate measuring apparatus is 1 ms. A method for starting the counting of the period measuring counter upon the receipt of the velocity pulse has been adopted in recently available inverter units.
Some recently available inverter units are adapted to set the measuring period of the digital angular velocity as short as approximately 1 ms. An external disturbance torque observer control using difference of the measured value (differential value) on the high-speed measuring period is carried out in these recently available inverter units. However, sufficient angular acceleration resolution cannot be obtained from the differential value described above and either a moving average or a filter process is therefore required.
In a simple angular velocity variation rate measuring system in which the number of velocity pulse inputted within a measurement period are counted and the counted number of the velocity pulses are multiplied by a certain coefficient, the number of velocity pulses inputted within the period of 10 milliseconds exceed slightly 100 even if the number of output pulses per revolution of the rotary axle are set to 10,000 or more. Hence, the angular velocity measuring apparatus is inappropriate for the angular velocity variation rate measurement.
In addition to the pair of pulse pick-ups and inductor, the pair of velocity pulse generators includes a pair of optical rotary encoders, the disc shaped plate (viz., the encoder main body) being attached onto the rotary axle. The rotary encoder includes disc shaped plate on a circumference of which a plurality of equally spaced slits are arranged, the disc shaped plate being attached on the rotary axle, and a pair of photo couplers, one of the photo couplers being disposed in an approximately 180xc2x0 phase difference with the other.
A special assembly part in which the pair of photo couplers are built is used. However, the presence of an inherent eccentricity of a peripheral wall of the slit plate attached around the rotary axle due to a manufacturing accuracy has a detrimental effect on the measured result of the velocity variation rate or angular acceleration. Consequently, one variation in the measured revolution variation rate per revolution of the rotary axle occurs.
It was determined that the variation in the velocity variation rate occurs due to a pitch error in the gear portion of the inductor as a result of a performance verification carried out for a sample of the previously proposed digital angular velocity variation rate measuring apparatus including the inductor, the pair of velocity pulse generators and the first angular velocity variation rate calculating section.
Since the analog differentiator is operated under an extremely high amplification factor, an anti-oscillation amplification capacitor to prevent a self-oscillation needs to be inserted into a feedback loop in the differentiator. This insertion of the oscillation-preventing capacitor reduces the response frequency. On the other hand, the digital angular velocity variation rate calculating section has a possibility of obtaining the response frequency as several times as the analog differentiator. However, it is necessary to reduce the response frequency due to a presence of the pitch error on the gear position of the inductor. It is noted that the pitch error is an error present in a pitch diameter of such a toothed gear type inductor as described above.
It was determined from various experiments that the pitch error occurs with an optical slit plate, such as that used in an optical rotary encoder, as well as with toothed gear type inductors. It was also determined that the output variation in the angular velocity variation rate occurred by an odd number of times per revolution. For example, when the toothed gear type inductor was used as the component of the pulse generator pair in a full electric inertia control chassis dynamometer, the output variation of the angular velocity variation rate or angular acceleration (dv/dt) occurred four times per revolution period. As a result, the angular velocity variation rate (dv/dt) was indicated by a roller peripheral velocity variation rate in m/s2 which is multiple of the angular acceleration (rad/s2) of a roller radius (m).
In the case of the optical rotary encoder, the output variation of the angular velocity variation rate occurred either two or six times per revolution.
In addition, a variation waveform of the angular velocity variation rate was sinusoidal and a main frequency component of the variation waveform was 29.17 Hz when the roller peripheral velocity was 100 km/h, the roller revolution was 7.292sxe2x88x921 (x4=29.19sxe2x88x921).
The number of times by which the waveform variation occurrence is proportional to a square of the revolution velocity (or angular velocity) in the same way as the variation due to the eccentricity of the inductor.
In the case of the use of the toothed gear type inductor, it was empirically determined that the number of times the variation in the angular velocity variation rate occurred was reproducible if a working facility were the same and dimension and the number of tooth were also the same.
When the optical rotary encoder is used, the slit plate is manufactured with a photo-resist sensor (a pair of photo couplers). Hence, if the same structure, the same manufacturing form, and the same number of generated pulse number were produced, the number of variations in the velocity variation rate is reproducible.
It is, therefore, an object of the present invention to provide an improved apparatus for measuring the angular velocity variation rate of the rotary axle with a high accuracy which can suppress the output variation in the angular velocity variation rate due to at least the eccentricity of the toothed gear type inductor, the optical slit plate the pitch error in the toothed gear portion or in the slit portion of the slit plate.
According to one aspect of the present invention, there is provided with an apparatus for measuring an angular velocity variation rate of a rotary axle, comprising: an approximately circular disc shaped plate attached approximately concentrically around the rotary axle, the approximately circular disc shaped plate including a plurality of approximately equally spaced apart projections on a circumference thereof; a first pair of velocity pulse generators, each velocity pulse generator of the first pair being disposed around the circumference of the plate on a first virtual line passing through a center of the rotary axle with one of the velocity pulse generators positioned at a 180xc2x0 revolution difference with respect to the other and generating a corresponding one of first and second velocity pulse signals in synchronization with a revolution of the plate; a first couple of angular velocity measuring sections that measure an angular velocity of the rotary axle from the corresponding one of first and second velocity pulse signals outputted by the first pair of the velocity pulse generators and outputs first and second angular velocity indicative signals each one indicating the measured angular velocity of the rotary axle independently of the other; a first average angular velocity measuring section that calculates an average value of the first and second angular velocity indicative signals outputted by the first couple of angular velocity measuring sections and outputs a first averaged angular velocity indicative signal indicating the average value of the first and second angular velocity indicative signals; a second pair of velocity pulse generators, each velocity pulse generator of the second pair being disposed around the circumference of the plate on a second virtual line passing through the center of the rotary axle at an angle of 180xc2x0/m to the first virtual line when a variation in the angular velocity variation rate indicative signal occurs m-th number of times per revolution of the rotary axle and generating a corresponding one of third and fourth velocity pulse signals in synchronization with the revolution of the plate; a second couple of angular velocity measuring sections that measure the angular velocity of the rotary axle from the corresponding one of third and fourth velocity pulse signals outputted by the second pair of the velocity pulse generators and output third and fourth angular velocity indicative signals each one indicating the measured angular velocity of the rotary axle independently of the other; a second average angular velocity measuring section that calculates an average value of the third and fourth angular velocity indicative signals outputted by the second couple of angular velocity measuring sections and outputs a second averaged angular velocity indicative signal indicating the average value of the third and fourth angular velocity indicative signals; and a differentiating section that differentiates a signal based on at least one of the first and second averaged angular velocity indicative signals outputted by the first and second average angular velocity measuring sections to output the angular velocity variation rate indicative signal.
According to another aspect of the present invention, there is provided with an apparatus for measuring an angular velocity variation rate of a rotary axle, comprising: an approximately circular disc shaped plate attached approximately concentrically around the rotary axle, the approximately circular disc shaped plate including a plurality of approximately equally spaced apart projections on a circumference thereof; a first pair of velocity pulse generators, each velocity pulse generator of the first pair being disposed around the circumference of the plate on a first virtual line passing through a center of the rotary axle with one of the velocity pulse generators positioned in a 180xc2x0 rotational difference with respect to the other and generating a corresponding one of first and second velocity pulse signals in synchronization with a revolution of the plate; a first couple of angular velocity measuring sections that measure an angular velocity of the rotary axle from the corresponding one of first and second velocity pulse signals outputted by the first pair of the velocity pulse generators and outputs first and second angular velocity indicative signals each one indicating the measured angular velocity of the rotary axle independently of the other; a first average angular velocity measuring section that calculates an average value of the first and second angular velocity indicative signals outputted by the first couple of angular velocity measuring sections and outputs a first averaged angular velocity indicative signal indicating the average value of the first and second angular velocity indicative signals; a second pair of velocity pulse generators, each velocity pulse generator of the second pair being disposed around the circumference of the plate on a second virtual line passing through the center of the rotary axle and being inclined at an angle of 180xc2x0/m to the first virtual line set when a variation in the angular velocity variation rate indicative signal occurs m-th number of times per revolution of the rotary axle and generating a corresponding one of third and fourth velocity pulse signals in synchronization with the revolution of the plate; a second couple of angular velocity measuring sections that measure the angular velocity of the rotary axle from the corresponding one of third and fourth velocity pulse signals outputted by the second pair of the velocity pulse generators and output third and fourth angular velocity indicative signals each one indicating the measured angular velocity of the rotary axle independently of the other; a second average angular velocity measuring section that calculates an average value of the third and fourth angular velocity indicative signals outputted by the second couple of angular velocity measuring sections and outputs a second averaged angular velocity indicative signal indicating the average value of the third and fourth angular velocity indicative signals; a first differentiator that differentiates the first averaged velocity indicative signal to output a first angular velocity variation rate indicative signal; a second differentiator that differentiates the second averaged velocity indicative signal to output a second angular velocity variation rate indicative signal; and an average value calculator that calculates an average value of the first and second averaged angular velocity variation rate indicative signals to output the angular velocity variation rate indicative signal.
According to a still another object of the present invention, there is provided with An apparatus for measuring an angular velocity variation rate of a rotary axle, comprising: an approximately circular disc shaped plate attached approximately concentrically around the rotary axle, the approximately circular disc shaped plate including a plurality of approximately equally spaced apart projections on a circumference thereof; a first pair of velocity pulse generators, each velocity pulse generator of the first pair being disposed around the circumference of the plate on a virtual line passing through a center of the rotary axle with one of the velocity pulse generators positioned in a 180xc2x0 rotational difference with respect to the other and generating a corresponding one of first and second velocity pulse signals in synchronization with a revolution of the plate; a first couple of angular velocity measuring sections that measure an angular velocity of the rotary axle from the corresponding one of first and second velocity pulse signals outputted by the first pair of the velocity pulse generators and outputs first and second angular velocity indicative signals each one indicating the measured angular velocity of the rotary axle independently of the other; a first average angular velocity measuring section that calculates an average value of the first and second angular velocity indicative signals outputted by the first couple of angular velocity measuring sections and outputs a first averaged angular velocity indicative signal indicating the average value of the first and second angular velocity indicative signals; a second pair of velocity pulse generators, each velocity pulse generator of the second pair being disposed around the circumference of the plate on a second virtual line passing through the center of the rotary axle and being inclined at an angle of 180xc2x0/m to the first virtual line set when a variation in the angular velocity variation rate indicative signal occurs m-th number of times per revolution of the rotary axle and generating a corresponding one of third and fourth velocity pulse signals in synchronization with the revolution of the plate; a second couple of angular velocity measuring sections that measure the angular velocity of the rotary axle from the corresponding one of third and fourth velocity pulse signals outputted by the second pair of the velocity pulse generators and output third and fourth angular velocity indicative signals each one indicating the measured angular velocity of the rotary axle independently of the other; a second average angular velocity measuring section that calculates an average value of the third and fourth angular velocity indicative signals outputted by the second couple of angular velocity measuring sections and outputs a second averaged angular velocity indicative signal indicating the average value of the third and fourth angular velocity indicative signals; a third average angular velocity measuring section that calculates a further average angular velocity measuring section that calculates a further average value of the first and second averaged velocity indicative signals and outputs a fourth averaged angular velocity indicative signal indicating the fourth average value; and a differentiator that differentiates the further average indicative signal to output the angular velocity variation rate indicative signal.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.